(1) Field of the Invention
The present invention relates to an aircraft having both a rotary wing and a fixed wing. The invention thus lies in the particular technical field of rotorcraft.
More particularly, the invention relates to an aircraft capable of vertical takeoff and landing, which is able to land on an offshore platform for the purpose of ferrying passengers and goods to and from the platform.
(2) Description of Related Art
In order to understand clearly the object of the invention and the specific nature of the technical field concerned, it should be recalled that most flying machines are either airplanes or rotorcraft.
The term “airplane” is used to designate any aircraft for which lift is provided by at least one fixed wing, also referred to as a pair of half-wings. The wing may be continuous in the form of two half-wings that are secured to each other and that extend through the fuselage, or it may be discontinuous, being in the form of two distinct half-wings.
Various techniques are known for reducing the span of the fixed wing and for diminishing its airfoil drag in a longitudinal direction of the aircraft.
In particular, aircraft are known that have at least one closed wing, i.e. a wing that is circular or annular in shape surrounding the fuselage of the airplane.
According to the literature, such a closed wing may give rise to instability in pitching. Reference may be made to the Wikipedia article “aile en anneau”, May 30, 2011, XP002673698, taken from the Internet at URL:
http://fr.wikipedia.org/wiki/Aile_en_anneau
[http://en.wikipedia.org/wiki/Closed_wing].
Furthermore, the term “rotorcraft” designates any aircraft in which lift is provided in full or in part by a rotary wing. A rotary wing comprises at least one lift rotor of large diameter arranged above the fuselage.
In the rotorcraft category, there is the autogyro in which the main rotor does not receive power, but autorotates under the effect of the forward speed of the aircraft.
The category of rotorcraft also includes the helicopter in which at least one main rotor driven by a suitable power plant provides both lift and propulsion.
A helicopter can land on an offshore oil platform without difficulty. Nevertheless, the forward speed of a conventional helicopter is low, which prevents it from achieving large ranges, and thus reaching oil platforms that are far away from the shore.
In order to remedy that, various other novel formulas have been studied specifically, and some of them have given rise to practical embodiments.
In particular, aircraft are known that have a rotary wing above the fuselage of the aircraft and a fixed wing for achieving a relatively high forward speed.
Nevertheless, it is found that at low speed and in particular while hovering, the fixed wing presents non-negligible airfoil drag in an elevation direction of the aircraft. This can lead to potential degradation of performance during such stages of flight.
It can be understood that this problem is specific to the very narrow technical field of aircraft having a rotary wing above a fixed wing.
Document WO 2008/003455 proposes an aircraft having a wing made up of two half-wings that are movable in a horizontal plane.
Document US 2007/095970 describes an aircraft having at least one pivoting fixed-wing.
Document DE 20303024 describes an aircraft provided with top and bottom canard type lift planes. The bottom plane is not situated in the wake of the top plane, given the way the planes are arranged.
Document FR 2 952 612 describes a fixed-wing aircraft having both a forward wing and an aft wing.
Document FR 616 764 discloses an aircraft having two contrarotating propellers, a top fixed lift plane and a bottom fixed lift plane.
The following documents are also known: U.S. Pat. No. 1,719,048, GB 274 534, FR 550 679.